Typical examples of a conventionally known green pigment include a polyhalogenated copper phthalocyanine. Since this polyhalogenated copper phthalocyanine has excellent fastness properties but has a large amount of halogen atoms such as chlorine and bromine atoms in the molecule, there have some fear for the safety and environmental burden, recently. Therefore, it is required to develop a pigment capable of coloring green with a compound having no halogen atom.
As a method of coloring green with a compound having no halogen atom (hereinafter referred to as “halogen-free”), for example, there is proposed a method comprising mixing copper phthalocyanine as a blue pigment with a yellow organic pigment, thereby performing toning to obtain a green pigment, and using the resulting green pigment (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 2001-64534). However, this method causes a problem that segregation occurs because two kinds of pigments, each having a quite different chemical structure, are mixed, and also causes a problem that hue remarkably varies when exposed to sunlight because light resistance varies depending on the kind of the pigment mixed.
On the other hand, as a halogen-free compound which has green hue itself for example, a phthalocyanine compound having an imidazole ring represented by the following general formula (a) (hereinafter referred to as a “compound (a)”) (see, for example, Russian Journal of General Chemistry, 69 (8), 1321 (1999) and Journal of Porphyrins and Phthalocyanines, 4, 505 (2000)). However, the above problem such as segregation is solved by the compound (a) in this method, but there was a problem that resistance to an organic solvent or an acid is insufficient
wherein M represents a copper atom or two hydrogen atoms, and Ra represents any one of a hydrogen atom, a methyl group, and a benzyl group.